My 7 year old son has always been the same - he has spent a lot of his time on the step! He would deliberately engineer himself into a tantrum - I think he genuinely enjoys them. They are getting fewer as the years go by. My 8 year son only ever had about 2, we ignored them and he has never bothered since. With my younger son we tried the step, time out, ignoring them, losing priviledges, rewards for good behaviour etc etc etc.
We do know that he can control it, as at school he is an angel and "a pleasure to teach". He is very bright and needs to have a lot of intellectual stimulation. As sleepy says, he does combine it by being very affectionate which does make up for it in some way.
As I said, the tantrums are getting less and less as he is able to compute that it is not worth losing a week of play station for - and he hasn't banged his head off the pavement since he was about 2! Another thing that really brought it home to him was filming him having a tantrum and showing him how ridiculous he looked. he now believes us when we say that he is behaving like a giant two year old. This may not work with yours yet, but it is worth a try.
You need to be firm - use all known diversion/ punishment tactics and never, ever give in and it will gradually decline. If you know that you are going to give in, then do it straight away as then they learn that sometimes they can win, but that you wont give in if they keep persisting.
I also love the toddler taming book by Christopher Green - its worth a read.
Good luck!